High selective parallel‐scheme filtering antenna synthesized by transversal coupling matrix

Abstract

A novel synthesis method based on transversal coupling matrix for the parallel-scheme filtering antenna with high out-of-band selectivity is proposed. The filtering antenna consists of three resonant radiation elements that are connected to a common feed point. By adopting the parallel scheme, the design of a third-order filtering antenna can be decomposed into three first-order sub filtering antennas. Each resonant antenna element can be separately designed and little adjustment is needed after combining these elements. Given a specification with up to two radiation nulls, the corresponding parameters of the three elements can be synthesized using the coupling matrix theory based on transversal topology. A practical filtering antenna centered at 5.74 GHz with the bandwidth of 410 MHz (7.2%) and two radiation nulls at 5.43 GHz and 6.13 GHz is fabricated. The measurements show the gain of 7.5 dBi and out-of-band suppression more than 30 dB at both passband sides can be achieved within the total size of 1.208λ0 × 1.725λ0 × 0.024λ0, where λ0 is the free space wavelength of the center frequency.